Filters are useful in a variety of contexts. For example, filters are often used in electrical or optical equipment. An air pressure differential between the interior and exterior of a housing containing the equipment can be produced as the electrical or optical equipment heats and cools. Often the housing includes a vent to allow air flow that equalizes the pressure. A filter is typically provided over the vent to reduce the flow of contaminants into the housing.
Computer disk drives, and in particular, hard disk drives, are one example of a device that uses filters in this manner. Disk drives are sensitive to moisture, chemical contamination, and particulate contamination, particularly, as the drive heads become smaller and aerial densities increase. Chemical contaminants, such as hydrocarbons and acid gases, can condense onto a disk and degrade the head/disk interface and corrode the heads. Particulate contaminants can lead to stiction and can cause read/write errors and head crashes.
It has been found that particulate and gaseous contaminants act to reduce efficiency and longevity of hard disk drives. Common sources of contaminants in disk drives include leaks (which may or may not be intentional), the manufacturing environment, and the materials incorporated into the disk drive which give off particulates and gases. It is of particular concern that organic vapors can be generated inside disk drive enclosures during normal operating conditions when, for example, the temperature exceeds 150° F. (about 65° C.). Such temperatures can be achieved by simply leaving the computer in the trunk of a car on a hot day or during operation.
Breather and recirculation filters have been used in hard disk drives for removing contaminates. Typically, recirculation filters have been included to remove unwanted particulates. They are not, however, typically suitable for removing organic vapors since they do not have a capacity for permanently adsorbing organic vapors. To provide enhanced organic vapor removal, activated carbon or other adsorbent material has been used in recirculation filters as well as breather filters. For example, activated carbon in the form of granules or fiber can adsorb and remove organic vapors from the air within a disk drive housing.